The mammalian tachykinins, also known as neurokinins, are a family of small peptides that share a common carboxyl-terminal sequence of Phe-X-Gly-Leu-Met-NH2 (Maggio et al., Annual Rev. Neuroscience 11:13-28 (1998). The main members of the family are substance P (SP), neurokinin A (NKA) and neurokinin B (NKB). As neurotransmitters these peptides exert their biological activity via three distinct neurokinin (NK) receptors termed neurokinin-1 (NK1), neurokinin-2 (NK2) and neurokinin-3 (NK3). SP binds preferentially to NK1, NKA to NK2 and NKB to NK3. The NK3 receptor is characterized by a predominant expression in the central nervous system (CNS) and its involvement in the modulation of the central monoaminergic (noradenaline and dopamine) and amino acid (GABA) neurotransmission. These properties make the NK3 receptor a potential target for CNS diseases such as schizophrenia (Spooren et al., Nat. Rev. Drug Discov. 4:967-975 (2005).
Schizophrenia is a chronic, severe, and disabling brain disorder that affects about 1% of the world's population. Symptoms begin in early adulthood and are followed by a period of interpersonal and social dysfunction. The symptoms of schizophrenia fall into three broad categories: positive symptoms, negative symptoms, and cognitive symptoms. Positive symptoms include hallucinations, delusions, thought disorders and movement disorders. Negative symptoms include depression, anhedonia, blunted affect, diminished speech and cognitive symptoms include memory and attention deficits as well as social withdrawal.
There is no single cause of schizophrenia however, increased dopamine activity in the mesolimbic pathway of the brain is consistently found in schizophrenic individuals. The lack of knowledge about the exact cause and nature of this disease make development of new drugs difficult. Treatment has been focused on antipsychotic medication which primarily works by suppressing dopamine activity. As these drugs have evolved through the years the side effect profile has improved but they still exhibit some side effects such as weight gain. In 2004 Sanofi-Synthelabo published clinical results for Osanetant which was identified as a potent and selective antagonist of the NK3 receptor for the treatment of schizophrenia and in 2005 GSK published clinical results for talenant which was shown to ameliorate the cognitive issues of schizophrenics however, both compounds have poor pharmacokinetics and pharmacodynamic properties including poor solubility, poor bioavailability, relatively high clearance and poor brain-blood barrier penetration. In spite of the liabilities with these compounds, clinical results to date suggest that the NK3 receptor may prove to be a promising target for treatment of schizophrenia providing that pharmacokinetic and pharmacodynamic issues can be resolved.
Irritable bowel syndrome (IBS) is a chronic, episodic functional gastrointestinal (GI) disorder characterized by abdominal pain/discomfort and altered bowel habit (constipation, diarrhea or alternating periods of both). Patients often experience additional symptoms such as bloating, sensation of incomplete evacuation, straining (constipation) and urgency (diarrhea). IBS patients can experience symptoms for many years, with an average duration of 10 or more years. IBS is often unrecognized or untreated, with as few as 25% of IBS sufferers seeking professional health care. IBS prevalence is estimated to be up to 20% of the population. Functional bowel disorders such as IBS are characterized by visceral hypersensitivity defined by reduced pain and discomfort thresholds, which may manifest as pain associated with bowel disturbances (Akbar et al., Alimentary Pharmacology and Therapeutics, 30(5): 423-435 (2009). Although the pathogenesis of visceral hypersensitivity is not fully understood, several mechanisms have been proposed including subtle inflammation, psychosocial factors and altered sensorimotor function of the gut, a major component of which is believed to be peripheral and central sensitization of visceral afferent neuronal pathways. Similarly, the other functional bowel disorders such as noncardiac chest pain, functional dyspepsia and functional abdominal pain present commonly and treatment of these disorders can be challenging. Over the past 30 years, the main treatment of irritable bowel syndrome has aimed to normalize gastrointestinal transit using either laxatives or antidiarrheal agents, with or without the concurrent use of spasmolytics. These therapeutic options are limited and often disappointing in efficacy.
Recent investigation into the pathophysiology of irritable bowel syndrome has focused on evaluation of visceral hypersensitivity (Bueno et al. Gut, 51 (Suppl):19-23 (2002). At the same time, more information has been acquired on the status of the local immune system as a possible cause for sensitization of nerve terminals. Such investigations have stimulated the emergence of new concepts and original candidate drugs for the treatment of this functional disorder.
Tachykinin receptors do not appear to play significant roles in normal GI functions, but may be involved in defensive or pathological processes. NK3 receptors have been found to mediate certain disruptions of intestinal motility. The activity may be driven by tachykinins released from intrinsic primary afferent neurones (IPANs), which induce slow excitatory postsynaptic potential (EPSP) activity in connecting IPANs and hence, a degree of hypersensitivity within the enteric nervous system. The same process is also proposed to increase C-fibre sensitivity, either indirectly or directly. Thus, NK3 receptor antagonists inhibit intestinal nociception via a “peripheral” mechanism that may be intestine-specific. Studies with talnetant and other selective NK3 receptor antagonists revealed an exciting and novel pathway by which pathological changes in intestinal motility and nociception can be induced, suggesting a role for NK3 receptor antagonism in irritable bowel syndrome (Sanger, Brit. J. of Pharm., 141:1303-1312 (2004)).
The chemical compound nitric oxide is a gas with chemical formula NO. NO is one of the few gaseous signaling molecules known in biological systems, and plays an important role in controlling various biological events. For example, the endothelium uses NO to signal surrounding smooth muscle in the walls of arterioles to relax, resulting in vasodilation and increased blood flow to hypoxic tissues. NO is also involved in regulating smooth muscle proliferation, platelet function, neurotransmission, and plays a role in host defense. Although nitric oxide is highly reactive and has a lifetime of a few seconds, it can both diffuse freely across membranes and bind to many molecular targets. These attributes make NO an ideal signaling molecule capable of controlling biological events between adjacent cells and within cells.
NO is a free radical gas, which makes it reactive and unstable, thus NO is short lived in vivo, having a half life of 3-5 seconds under physiologic conditions. In the presence of oxygen, NO can combine with thiols to generate a biologically important class of stable NO adducts called S-nitrosothiols (SNO's). This stable pool of NO has been postulated to act as a source of bioactive NO and as such appears to be critically important in health and disease, given the centrality of NO in cellular homeostasis (Stamler et al., Proc. Natl. Acad. Sci. USA, 89:7674-7677 (1992)). Protein SNO's play broad roles in cardiovascular, respiratory, metabolic, gastrointestinal, immune and central nervous system function (Foster et al., 2003, Trends in Molecular Medicine Volume 9, Issue 4, April 2003, pages 160-168). One of the most studied SNO's in biological systems is S-nitrosoglutathione (GSNO) (Gaston et al., Proc. Natl. Acad. Sci. USA 90:10957-10961 (1993)), an emerging key regulator in NO signaling since it is an efficient trans-nitrosating agent and appears to maintain an equilibrium with other S-nitrosated proteins (Liu et al., Nature, 410:490-494 (2001)) within cells. Given this pivotal position in the NO-SNO continuum, GSNO provides a therapeutically promising target to consider when NO modulation is pharmacologically warranted.
In light of this understanding of GSNO as a key regulator of NO homeostasis and cellular SNO levels, studies have focused on examining endogenous production of GSNO and SNO proteins, which occurs downstream from the production of the NO radical by the nitric oxide synthetase (NOS) enzymes. More recently there has been an increasing understanding of enzymatic catabolism of GSNO which has an important role in governing available concentrations of GSNO and consequently available NO and SNO's.
Central to this understanding of GSNO catabolism, researchers have recently identified a highly conserved S-nitrosoglutathione reductase (GSNOR) (Jensen et al., Biochem J., 331:659-668 (1998); Liu et al., 2001). GSNOR is also known as glutathione-dependent formaldehyde dehydrogenase (GS-FDH), alcohol dehydrogenase 3 (ADH-3) (Uotila and Koivusalo, Coenzymes and Cofactors., D. Dolphin, ed. pp. 517-551 (New York, John Wiley & Sons, 1989)), and alcohol dehydrogenase 5 (ADH-5). Importantly GSNOR shows greater activity toward GSNO than other substrates (Jensen et al., 1998; Liu et al., 2001) and appears to mediate important protein and peptide denitrosating activity in bacteria, plants, and animals. GSNOR appears to be the major GSNO-metabolizing enzyme in eukaryotes (Liu et al., 2001). Thus, GSNO can accumulate in biological compartments where GSNOR activity is low or absent (e.g. airway lining fluid) (Gaston et al., 1993).
Yeast deficient in GSNOR accumulate S-nitrosylated proteins which are not substrates of the enzyme, which is strongly suggestive that GSNO exists in equilibrium with SNO-proteins (Liu et al., 2001). Precise enzymatic control over ambient levels of GSNO and thus SNO-proteins raises the possibility that GSNO/GSNOR may play roles across a host of physiological and pathological functions including protection against nitrosative stress wherein NO is produced in excess of physiologic needs. Indeed, GSNO specifically has been implicated in physiologic processes ranging from the drive to breathe (Lipton et al., Nature, 413:171-174 (2001)) to regulation of the cystic fibrosis transmembrane regulator (Zaman et al., Biochem Biophys Res Commun, 284:65-70 (2001), to regulation of vascular tone, thrombosis and platelet function (de Belder et al., Cardiovasc Res. 1994 May; 28(5):691-4. (1994); Z. Kaposzta, A et al., Circulation; 106(24): 3057-3062, 2002) as well as host defense (de Jesus-Berrios et al., Curr. Biol., 13:1963-1968 (2003)). Other studies have found that GSNOR protects yeast cells against nitrosative stress both in vitro (Liu et al., 2001) and in vivo (de Jesus-Berrios et al., 2003).
Collectively data suggest GSNOR as a primary physiological ligand for the enzyme S-nitrosoglutathione reductase (GSNOR), which catabolizes GSNO and consequently reduces available SNO's and NO in biological systems (Liu et al., 2001), (Liu et al., Cell, (2004), 116(4), 617-628), and (Que et al., Science, 2005, 308, (5728):1618-1621). As such, this enzyme plays a central role in regulating local and systemic bioactive NO. Since perturbations in NO bioavailability has been linked to the pathogenesis of numerous disease states, including hypertension, atherosclerosis, thrombosis, asthma, gastrointestinal disorders, inflammation and cancer, agents that regulate GSNOR activity are candidate therapeutic agents for treating diseases associated with nitric oxide imbalance.
Currently, there is a great need in the art for diagnostics, prophylaxis, ameliorations, and treatments for medical conditions relating to a disease or condition characterized by overstimulation of NK3. There is also a need in the art for diagnostics, prophylaxis, ameliorations, and treatments for medical conditions relating to a disease or condition characterized by increased NO synthesis and/or increased NO bioactivity. In addition, there is a significant need for novel compounds, compositions and methods for preventing, ameliorating, or reversing other NK3 associated disorders and/or other NO-associated disorders. The present invention satisfies these needs.